Thermionic tube



Jan. 5 1926.

F. S. M CULLOUGH THERMI ONI C TUBE Filed y 6, 1925 IN VEN TOR.

ATTORNEY PATENT OFFICE.

FREDERICK S. HOCULIDUGH, OI WILKINSBUBG, I'ENNSYLVANIA.

'rrmainomo TUBE.

Application filed Kay 8,

To all whom it may concern:

Be it known that I, FREDERICK S. McConmuen, a citizen of the United States, residing at Wilkinsburg, in the county of Allegheny and State of Penns lvania, have invented certain new and use 111 Improvements in Thermionic Tubes, of which the followin is a specification.

his invention is for an im rovement in thermionic tubes or. hot cathocfe devices.

The resent invention has for its object to provide, in a cathode device of this kind, a cathode which may be heated by alternatin or pulsating currents, sothat ordinary ouse lighting current may be emploged in the operation of the tubes. .This cat ode is so constructed as to produce no perceptible hum or noise or current variation in the circuit in which it is employed, due to the fluctuating field set up by such alternating current, provided, of course, that the voltage of such alternating or pulsating current is properly maintained with respect to the construction of the tube.

The invention may be readily understood by reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic sectional view of a. tube and a simple circuit embodying same;

Fig. 2 is a similar, view oi a slightly different circuit;

Fig. 3 is a detail view, showing on a larger scale the construction of the cathode.

In the drawings, I have illustrated conventionally a three electrode type of tube, but the invention is not restricted to any particular tube construction or type of tube.

In the drawings, 5 designates a suitable envelo e containing a plate or anode 6. Inside t e anode, as usually arranged, is a 'd or control electrode 7. Inside the grid and out of contact therewith is the cathode.

The cathode construction includes a body or rod 8 of porcelain or other suitable material in which is enclosed a resistance heater 9 havin lead wires 10 extending out of the top of t e tube, these wires being connected in an alternating current circuit, which may include a step-down transformer 11 to maintain the volta e at a proper valuefor the construction 0 the tube.

Surrounding the rod,- and -preferably ti htly fitted thereto, is an inner sleeve 12 of a magnetic nature, such as nickel or .cop-

per. On the outsideof this sleeve is a thm current values in the alternatin vent the oscillating field 1925. Serial No. 28,341.

coating of heat resistant enamel or insulation 13, and fitted over this is an outer sleeve 14 which is the actual cathode and which preferably has a coating of a high emission character.

I The heater wires are preferably co-extensive with the porcelain rod, and the inner sleeve. 12 is preferably slightly longer than the cathode 14 and extends above and below the cathode.

In operation, the tube may be connected in any standard or preferred circuit, and the magnetic shield 12 may be grounded through lead wire 12. The heater is ener- 'gized, and this in turn heats the porcelain rod and the rod acts as a heat reservoir so that the temperature of the cathode will not fluctuate with the maximum and minimum heating circuit. The heat from'the rod W1 1 be conducted through the inner sleeve 12 to the outer sleeve or cathode 14, raising it to an efiicient emitting temperature.

Provided that the voltage in the heater is properly proportioned, to the construction of the tube, the magnetic shield 12 will preroduced by the alternating heater current rom affecting in any manner the operation of the tube, so that no hum or alternating current fluctuation isj'apparent in the tube circuit. The grounded shield eliminates any generation of eddy currents in the cathode, and neutralizes the capacity between the heater wires and the cathode.

Instead of grounding the magnetic shield, it may be desirable to connect the cathode andthe shield through a potentiometer P, as shown in Fig. 2.

From the foregoing, it will be evident that the structures and circuits shown are for the purpose of illustration only, and

that various changes and modifications are to be considered as within the spirit of the present invention.

I claim as my invention;

1. A hot cathode device including an" anode, a control electrode, and a cathode structure, said cathode structure including a porcelain bod havin a heater therein, a shield associate with t e body, and a cathode element associated with the body, said shield being magnetically interposed between the heater and cathode element and out ofelectrical contact with the latter.

2. A hot cathode device including an anode, a cathode structure within the anode and out of contact therewith, said structure including a heat resistant rod having a heater element therein, a metallic sleeve surrounding the rod and having a heat resistant covering'thereon, and a cathode element fitted over the rod and sleeve and, insulated therefrom through said heat resistant covering.

3. A hot cathode device including an anode, a cathode structure within the anode and out of contact therewith, said structure including a. heat resistant rod having a heater element therein, a metallic sleeve surrounding the rod and having a heat resistant covering thereon, and a cathode element fitted overthe rod and sleeve and insulated therefrom through said heat resistant covering, said metallic .sleeve being longer than the said cathode element.

4. A hot cathode device including an anode, a cathode structure within the anode and out of contact therewith, said structure including a heat resistant rod having a heater element therein, a metallic sleeve surrounding the rod and having a heat resistant covering thereon and having an external connecting wire attached thereto, and a cathode element fitted over the rod and sleeve and insulated therefrom through said heat resistant covering.

In testimony whereof I hereunto aflix my signature.

FREDERICK S. MoCULLOUGH. 

